The invention relates to a check-valve construction and will be described in the context of such a valve, particularly suited to accommodation of unidirectional liquid flow, although it is in principle also applicable to check valves for fluids other than liquid.
The conventional check valve, as for unidirectional accommodation of liquid fuel when filling wing tanks of an aircraft, has one or two valve members or petals, spring-loaded for closure to a corresponding one or two valve seats. Each valve member has a pivotally hinged connection to associated valve-body structure, at a location of downstream and transverse offset from the valve seat, and the spring-loading is about the pivot axis of the valve member, as by passing the hinge pin through the center of a coil spring, with one tangential end arm referenced to the valve body and another tangential end arm preloading the valve member to closed position.
In a refueling valve of the character indicated, it is desirable to have a firm bias against valve opening, in order to avoid accidental loss of fuel during varying conditions of pressure drop across the valve member, as in high-G flight maneuvers, or when balancing the aircraft by transfer of fuel from one full tank to a more depleted tank. The traditional way to achieve such bias is to provide a more stiffly compliant, preloading spring of the character indicated. But while such a spring can elevate the force threshold required to commence valve-opening action, the fact remains that more force is required, the more the valve member is to be moved in the further-opening direction. A stiff spring of the character indicated thus necessarily imposes relatively great resistance to flow, and impairs the ability to achieve a maximum valve opening.